(1) Field of the Invention:
This invention relates to a flow change-over valve for the blowing of fluids into a molten metal vessel, and more particularly to a flow change-over valve which is advantageously used as a gas selecting valve when one of plural kinds of fluids (for instance, gaseous fluids containing powders which are unfavorable to be mixed with each other) is selectively blown into a bottom-blown converter with the change of times in the refining stage.
(2) Description of the Prior Art:
As a method of steel making and refining molten iron with a large amount of scrap in the bottom-blown converter, there has been proposed a technique in which a mixture of, for example, powdery coal and methane gas is blown into the converter through a part of bottom tuyeres and oxygen gas is simultaneously blown through the other remaining tuyeres to fuse the scrap, and after the inlet passage of the flow change-over valve is changed into another inlet passage, the resulting melt is refined by blowing oxygen gas containing powdery quicklime, etc. from such another inlet through the tuyeres used for the blowing of coal-containing methane gas as disclosed, for instance, in W. German Patent Application Publication No. 28 38 983 or Japanese Patent laid open No. 57-29,521.
In this refining method, the kind of the fluids to be blown into the converter should be changed with the change of times in the refining stage, which requires the use of a flow change-over valve. As the flow change-over valve satisfying this requirement, there is proposed a flow change-over valve of the following structure in Japanese Patent laid open No. 56-33,415. This is, it relates to an apparatus for introducing both finely powdered carbon-containing fuel floating in a carrier gas and oxygen into a molten iron vessel, characterized in that a movable valve member is arranged in a housing comprising a fuel supply pipe, an oxygen supply pipe and a tuyere pipe, and the valve member opens into a fuel hole section or an oxygen hole section and is actuated by the oxygen pressure inside the supply pipes.
In FIG. 1 is shown a vertical section view of the above apparatus (flow change-over valve), wherein numeral 2 is a movable valve member, numeral 4 a sealing portion, numeral 6 a fixed valve member, and numeral 8 bellows. In this type of the flow change-over valve, however, when the movable valve member 2 is moved toward the sealing portion 4 for closing, there are fears that the powder enters therein and that the hermetric property is deteriorated in a long-term use to disable the reliable change-over between two gases. Further, when the inlet passage is changed into another one in the flow change-over valve, if it is intended to use two gases to be prevented from mixing with each other, for instance, methane gas containing powdery coal and oxygen gas, there is a possibility that the above two gases are mixed with each other in the interior of the flow change-over valve. In the latter case, there is a risk that the coal in the gas is burned by the mixing of both gases to overheat the flow change-over valve. Moreover, there is also a danger that the overheating causes the deformation and burning of the sealing portion, resulting in the deterioration of the sealing. In addition, the bellows are worn out with the blown powder to be bored, so that an explosion is caused through the mixing of the two gases.